Methods and Systems for Presenting an Audio Signal to a Cochlear Implant Patient

ABSTRACT

An exemplary signal processing unit includes a plurality of filters configured to divide an audio signal into a plurality of analysis channels, one or more detection stages configured to detect an energy level within each of said analysis channels, a selection stage configured to select one or more of said analysis channels for presentation to a patient, a synthesizer stage configured to synthesize said selected analysis channels, and a mapping stage configured to map said selected analysis channels to a number of stimulation channels within an implantable cochlear stimulator, wherein a total number of said analysis channels is greater than a total number of said stimulation channels.

RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 11/858,649, filed Sep. 20, 2007, and entitled“Methods and Systems for Presenting an Audio Signal to a CochlearImplant Patient,” the contents of which are hereby incorporated byreference in their entirety.

BACKGROUND INFORMATION

The sense of hearing in human beings involves the use of hair cells inthe cochlea that convert or transduce acoustic signals into auditorynerve impulses. Hearing loss, which may be due to many different causes,is generally of two types: conductive and sensorineural. Conductivehearing loss occurs when the normal mechanical pathways for sound toreach the hair cells in the cochlea are impeded. These sound pathwaysmay be impeded, for example, by damage to the auditory ossicles.Conductive hearing loss may often be helped by the use of conventionalhearing aids that amplify sound so that acoustic signals reach thecochlea and the hair cells. Some types of conductive hearing loss mayalso be treated by surgical procedures.

Sensorineural hearing loss, on the other hand, is due to the absence orthe destruction of the hair cells in the cochlea which are needed totransduce acoustic signals into auditory nerve impulses. Thus, peoplewho suffer from sensorineural hearing loss are unable to derive anybenefit from conventional hearing aid systems.

To overcome sensorineural hearing loss, numerous cochlear implantsystems—or cochlear prosthesis—have been developed. Cochlear implantsystems bypass the hair cells in the cochlea by presenting electricalstimulation directly to the auditory nerve fibers. Direct stimulation ofthe auditory nerve fibers leads to the perception of sound in the brainand at least partial restoration of hearing function. To facilitatedirect stimulation of the auditory nerve fibers, an array of electrodesmay be implanted in the cochlea. The electrodes form a number ofstimulation channels through which electrical stimulation pulses may beapplied directly to auditory nerves within the cochlea.

Hence, an audio signal may be presented to a patient by processing andtranslating the audio signal into a number of electrical stimulationpulses. The stimulation pulses may then be applied directly to auditorynerves within the cochlea via one or more of the stimulation channels.

Typical cochlear implant systems also include an audio signal processor.The signal processor is configured to process an audio signal bydividing the audio signal into a number of frequency ranges or analysischannels with a number of band-pass filters. In typical cochlear implantsystems, the total number of analysis channels is equal to the totalnumber of stimulation channels.

However, it is often undesirable to present the signals contained withinall of the analysis channels to a patient at the same time. For example,if an incoming audio signal contains human speech in the presence of alot of background noise, the patient may not be able to distinguish thehuman speech from the background noise if all of the analysis channelsare presented to the patient simultaneously.

SUMMARY

Methods of presenting an audio signal to a cochlear implant patientinclude dividing the audio signal into a plurality of analysis channels,detecting an energy level within each of the analysis channels,selecting one or more of the analysis channels for presentation to thepatient, synthesizing the selected analysis channels, and mapping thesynthesized analysis channels to one or more stimulation channels.

Systems for presenting an audio signal to a cochlear implant patientinclude a signal processor and an implantable cochlear stimulatorcommunicatively coupled to the signal processor. The signal processor isconfigured to divide the audio signal into a plurality of analysischannels, detect an energy level within each of the analysis channels,select one or more of the analysis channels for presentation to thepatient, and synthesize the selected analysis channels. The implantablecochlear stimulator is configured to apply a stimulation current duringa stimulation frame to a cochlea of the patient via one or morestimulation channels in accordance with information contained within thesynthesized channels.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments of theprinciples described herein and are a part of the specification. Theillustrated embodiments are merely examples and do not limit the scopeof the disclosure.

FIG. 1 illustrates an exemplary cochlear implant system according toprinciples described herein.

FIG. 2 is a functional block diagram of an exemplary signal processorand implantable cochlear stimulator according to principles describedherein.

FIG. 3 illustrates an exemplary stimulation current pulse that may bedelivered to neural tissue via one or more stimulation channelsaccording to principles described herein.

FIG. 4 illustrates an exemplary audio signal in the frequency domainthat may be presented to a patient during a stimulation frame with acochlear implant system according to principles described herein.

FIG. 5 illustrates an exemplary signal processor wherein the number ofanalysis channels contained therein is greater than the number ofstimulation channels according to principles described herein.

FIG. 6 is a graphical illustration of a process of selecting,synthesizing, and mapping a number of analysis channels to correspondingstimulation channels according to principles described herein.

FIG. 7 illustrates the exemplary audio signal of FIG. 4 divided into 32analysis channels according to principles described herein.

FIG. 8 is a flow chart illustrating an exemplary method of presenting anaudio signal to a patient with a cochlear implant system according toprinciples described herein.

Throughout the drawings, identical reference numbers designate similar,but not necessarily identical, elements.

DETAILED DESCRIPTION

Methods and systems for presenting an audio signal to a cochlear implantpatient are described herein. A signal processor is configured to dividethe audio signal into a plurality of relatively narrow analysischannels, detect an energy level within each of the analysis channels,select one or more of the analysis channels for presentation to thepatient, and synthesize the selected analysis channels. An implantablecochlear stimulator may then apply a stimulation current representativeof the audio signal during a stimulation frame to a cochlea of thepatient via one or more broader stimulation channels in accordance withinformation contained within the synthesized channels. In some examples,the total number of analysis channels is greater than the total numberof stimulation channels. In this manner, the likelihood that relevantinformation within an audio signal will be detected and presented to apatient is increased.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present systems and methods. It will be apparent,however, to one skilled in the art that the present systems and methodsmay be practiced without these specific details. Reference in thespecification to “one embodiment” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment is included in at least one embodiment. Theappearance of the phrase “in one embodiment” in various places in thespecification are not necessarily all referring to the same embodiment.

FIG. 1 illustrates an exemplary cochlear implant system 100 that may beused in accordance with the present methods and systems. Exemplarycochlear implant systems suitable for use as described herein include,but are not limited to, those disclosed in U.S. Pat. Nos. 6,219,580;6,272,382; and 6,308,101, all of which are incorporated herein byreference in their respective entireties. The cochlear implant system100 of FIG. 1 includes a signal processor portion 101 and a cochlearstimulation portion 102. The signal processor portion 101 may include asignal processor (SP) 105, a microphone 103, and/or additional circuitryas best serves a particular application. The cochlear stimulationportion 102 may include an implantable cochlear stimulator (ICS) 107, anumber of electrodes 109 disposed on a lead 108, and/or additionalcircuitry as best serves a particular application. The components withinthe signal processor portion 101 and the cochlear stimulation portion102 will be described in more detail below.

The microphone 103 of FIG. 1 is configured to sense acoustic signals andconvert the sensed signals to corresponding electrical signals. Theelectrical signals are sent from the microphone 103 to the SP 105 via acommunication link 104. Alternatively, the microphone 103 may beconnected directly to, or integrated with, the SP 105. The SP 105processes these converted acoustic signals in accordance with a selectedsignal processing strategy to generate appropriate control signals forcontrolling the ICS 107. These control signals may specify or define thepolarity, magnitude, location (i.e., which electrode pair or electrodegroup receive the stimulation current), and timing (i.e., when thestimulation current is to be applied to a particular electrode pair) ofthe stimulation current that is generated by the ICS 107.

The lead 108 shown in FIG. 1 is configured to be inserted within a ductof the cochlea. As shown in FIG. 1, the lead 108 includes a multiplicityof electrodes 109, e.g., sixteen electrodes, spaced along its length. Itwill be understood, however, that any number of electrodes 109 may bedisposed on the lead 108. The lead 108 may be substantially as shown anddescribed in U.S. Pat. Nos. 4,819,647 or 6,129,753, each of which isincorporated herein by reference in its respective entirety. As will bedescribed in more detail below, electronic circuitry within the ICS 107is configured to generate and apply stimulation current to the cochleavia selected stimulation channels (i.e., pairs or groups of theindividual electrodes 109) in accordance with a specified stimulationpattern defined by the SP 105.

The ICS 107 and the SP 105 may be electronically connected via asuitable data or communication link 106. It will be understood that thedata communication link 106 may include a bi-directional communicationlink and/or one or more dedicated uni-directional communication links.

In some examples, the SP 105 and the microphone 103 comprise an externalportion of the cochlear implant system 100 and the ICS 107 and theelectrode lead 108 comprise an implantable portion of the system 100that is implanted within a patient's body. In alternative embodiments,one or more portions of the SP 105 are included within the implantableportion of the cochlear implant system 100.

The external and implantable portions of the cochlear implant system 100may each include one or more coils configured to transmit and receivepower and/or control signals via the communication link 106. Forexample, the external portion of the cochlear implant system 100 mayinclude an external coil (not shown) and the implantable portion of thecochlear implant system 100 may include an implantable coil (not shown).The external coil and the implantable coil may be inductively coupled toeach other, thereby allowing data to be transmitted therebetween. Thedata may include, for example, the magnitude and polarity of a sensedacoustic signal. The external coil may also transmit power from theexternal portion to the implantable portion of the cochlear implantsystem 100. It will be noted that, in some embodiments, both the SP 105and the ICS 107 may be implanted within the patient, either in the samehousing or in separate housings. If the SP 105 and the ICS 107 are inthe same housing, the communication link 106 may be realized with adirect wire connection within such housing. If the SP 105 and the ICS107 are in separate housings, the communication link 106 may include oneor more inductive links, for example.

FIG. 2 is a functional block diagram of an exemplary SP 105 and ICS 107.The functions shown in FIG. 2 are merely representative of the manydifferent functions that may be performed by the SP 105 and/or the ICS107. A more complete description of the functional block diagram of theSP 105 and the ICS 107 is found in U.S. Pat. No. 6,219,580, which isincorporated herein by reference in its entirety.

As shown in FIG. 2, the microphone 103 senses acoustic information, suchas speech and music, and converts the acoustic information into one ormore electrical signals. These signals are then amplified in audiofront-end (AFE) circuitry 121. The amplified audio signal is thenconverted to a digital signal by an analog-to-digital (A/D) converter122. The resulting digital signal is then subjected to automatic gaincontrol using a suitable automatic gain control (AGC) function 123.

After appropriate automatic gain control, the digital signal is thenprocessed in one of a number of digital signal processing or analysischannels 124. For example, the SP 105 may include, but is not limitedto, eight analysis channels 124. Each analysis channel 124 may respondto a different frequency content of the sensed acoustical signal. Inother words, each analysis channel 124 includes a band-pass filter(BPF1-BPFm) 125 or other type of filter such that the digital signal isdivided into m analysis channels 124. The lowest frequency filter may bea low-pass filter, and the highest frequency filter may be a high-passfilter.

As shown in FIG. 2, each of the m analysis channels 124 may also includean energy detection stage (D1-Dm) 126. Each energy detection stage 126may include any combination of circuitry configured to detect the amountof energy contained within each of the m analysis channels 124. Forexample, each energy detection stage 126 may include a rectificationcircuit followed by an integrator circuit. As will be described in moredetail below, the cochlear implant system 100 may be configured todetermine which of the m analysis channels 124 are presented to thepatient via the stimulation channels 129 by analyzing the amount ofenergy contained in each of the m analysis channels 124.

After energy detection, the signals within each of the m analysischannels 124 are forwarded to a mapping stage 127. The mapping stage 127is configured to map the signals in each of the m analysis channels 124to one or more of M stimulation channels 129. In other words, theinformation contained in the m analysis channels 124 is used to definethe stimulation current pulses that are applied to the patient by theICS 107 via the M stimulation channels 129. As mentioned previously,pairs or groups of individual electrodes 109 make up the M stimulationchannels.

In some examples, the mapped signals are serialized by a multiplexer 128and transmitted to the ICS 107. The ICS 107 may then apply stimulationcurrent via one or more of the M stimulation channels 129 to one or morestimulation sites within the patient's cochlea. As used herein and inthe appended claims, the term “stimulation site” will be used to referto a target area or location at which the stimulation current isapplied. For example, a stimulation site may refer to a particularlocation within the neural tissue of the cochlea. Through appropriateweighting and sharing of currents between the electrodes 109,stimulation current may be applied to any stimulation site along thelength of the lead 108.

FIG. 3 illustrates an exemplary stimulation current pulse 130 that maybe delivered to neural tissue via one or more of the stimulationchannels 129. The stimulation current pulse 130 of FIG. 3 is biphasic.In other words, the pulse 130 includes two parts—a negative first phasehaving an area A1 and a positive second phase having an area A2. In someimplementations, the negative phase A1 causes neural tissue todepolarize or fire. The biphasic stimulation pulse 130 shown in FIG. 3has an amplitude of 1 milliamp (ma) and a pulse width of 20 microseconds(μsec) for illustrative purposes only. It will be recognized that any ofthe characteristics of the stimulation pulse 130, including, but notlimited to, the pulse shape, amplitude, pulse width, frequency, burstpattern (e.g., burst on time and burst off time), duty cycle or burstrepeat interval, ramp on time, and ramp off time may vary as best servesa particular application. Moreover, the characteristics of thestimulation pulse 130 may be defined by the signal processor 105 as bestserves a particular application.

The biphasic stimulation pulse 130 shown in FIG. 3 is “charge balanced”because the negative area A1 is equal to the positive area A2. Acharge-balanced biphasic pulse is often employed as the stimulus tominimize electrode corrosion and charge build-up which can harmsurrounding tissue. However, it will be recognized that the biphasicstimulation pulse 130 may alternatively be charge-imbalanced as bestserves a particular application.

As mentioned, it is often undesirable to apply stimulation current viaall M stimulation channels to the cochlea of a patient at once or duringa single stimulation frame. For example, if an incoming audio signalcontains human speech in the presence of a lot of background noise, thepatient may not be able to distinguish the human speech from thebackground noise if stimulation current is applied via all M stimulationat once.

Hence, in some examples, a stimulation strategy known as an “N-of-M”strategy is used. In an N-of-M strategy, stimulation current is onlyapplied via N of the M stimulation channels during each stimulationframe, where N is less than M. For example, in some N-of-M strategies,the cochlear implant system 100 is configured to apply stimulationcurrent via a number of stimulation channels corresponding to the N“most relevant” stimulation channels. The N “most relevant” stimulationchannels may refer to the N stimulation channels with the highestdetected energy signals within the M stimulation channels. Toillustrate, if there are 8 stimulation channels (e.g., M is equal to 8and N is equal to 4, an exemplary N-of-M stimulation strategy selectsthe 4 highest energy-containing stimulation channels through whichstimulation current is applied during a particular stimulation frame.

However, N-of-M strategies result in portions of an incoming audiosignal being left out when the audio signal is presented to a patient inthe form of electrical stimulation via the N stimulation channels. Forexample, if only 4 stimulation channels are selected out of 8 possiblestimulation channels (i.e., N is equal to 4 and M is equal to 8, someinformation within the audio signal is lost when presented to thepatient. The lost information may sometimes include relevant information(e.g., speech) in the presence of irrelevant information (e.g.,background noise). As used herein, the term “relevant information” willbe used to refer to speech, music, or any other audio signal ofrelevance to a patient. The term “irrelevant information” will be usedherein to refer to portions of an audio signal that are not of relevanceto a patient such as, but not limited to, background noise.

An example will now be given in connection with FIG. 4 that illustrateshow relevant information within an audio signal may be lost while usingan N-of-M stimulation strategy. FIG. 4 illustrates an exemplary audiosignal 140 in the frequency domain that may be presented to a patientduring a stimulation frame with a cochlear implant system 100. As shownin FIG. 4, the audio signal 140 may be divided into eight analysischannels. However, it will be recognized that the audio signal 140 maybe divided into any number of analysis channels as best serves aparticular application. In some examples, each analysis channel shown inFIG. 4 is mapped to one of the stimulation channels 129 shown in FIG. 2.

The vertical axis in FIG. 4 represents the amount of signal energywithin each analysis channel. As shown in FIG. 4, each analysis channelcontains varying energy levels. In some examples, the energy detectionstages 126 within the signal processor 105 are configured to average thetotal amount of energy contained within each analysis channel. Thehorizontal dashed lines represent the average energy level containedwithin each analysis channel. An N-of-M stimulation strategy may then beused to select a number of analysis channels 124 for presentation to apatient that correspond to the N analysis channels that contain thehighest average energy levels.

For example, if N is equal to 4, an exemplary N-of-M stimulationstrategy may be used to select the four analysis channels with thehighest average energy levels for presentation to a patient. In theexample of FIG. 4, the four analysis channels with the highest averageenergy levels are channels 1, 4, 5, and 6.

In some instances, as described previously, relevant information may beincluded in one of the analysis channels that is not selected forpresentation to a patient. For example, channel 2 includes a narrow peak141 that may represent relevant information such as, but not limited to,human speech. However, because the energy detection stages 126 averagethe total amount of energy contained within each analysis channel, theaverage energy level of channel 2 may be lower than the average energylevels of the other channels (e.g., channels 1, 4, 5, and 6. Hence, anN-of-M stimulation strategy that selects channels 1, 4, 5, and 6 wouldresult in the relevant information represented by the peak 141 beinglost.

Hence, the systems and methods described herein may be used to preventrelevant information from being lost when an audio signal is presentedto a patient in the form of electrical stimulation. To this end, as willbe described in more detail below, the signal processor 105 includesmore analysis channels 124 than there are stimulation channels 129. Forexample, if the ICS 107 includes M stimulation channels 129, the signalprocessor 105 may include x*M analysis channels 124, where x is aninteger greater than zero and where the symbol “*” representsmultiplication. However, it will be recognized that the signal processor105 may include any number of analysis channels 124 that is greater thanthe number of stimulation channels 129.

FIG. 5 illustrates an exemplary signal processor 105 wherein the numberof analysis channels 124 contained therein is greater than the number ofstimulation channels 129. As shown in FIG. 5, M stimulation channels 129are coupled to the ICS 107 and x*M analysis channels 124 are includedwithin the signal processor 105. As will be described in more detailbelow, each of the M stimulation channels 129 may correspond to anynumber of analysis channels 124. For example, if x is equal to four,each stimulation channel 129 may correspond to four analysis channels124.

As shown in FIG. 5, each analysis channel 124 includes a band-passfilter 125 and a corresponding energy detection stage 126. Because thereare more analysis channels 124 than there are stimulation channels 129,the bandwidth of each of the analysis channels 124 is smaller than thebandwidth of each of the stimulation channels 129. For example, if thesignal processor 105 includes four analysis channels 124 for everystimulation channel 129, each analysis channel 124 has a bandwidth thatis one-fourth the bandwidth of each stimulation channel 129. In thismanner, as will be described in more detail below, the likelihood thatrelevant information within an audio signal will be detected andpresented to a patient is increased.

In some alternative examples, the signal processor 105 may be configuredto apply a masking function to the audio signal prior to detecting theenergy level within each analysis channel 124. The masking function maybe configured to filter the audio signal and remove portions thereofthat are not audible to normal listeners. A variety of techniques may beused to perform the masking function as may serve a particularapplication.

After the energy level within each analysis channel 124 is detected, achannel selector stage 150 may be configured to select one or moreanalysis channels 124 for presentation to the patient. In other words,information contained within the one or more analysis channels 124 thatare selected by the channel selection stage 150 is used to definestimulation current that is applied to the patient via one or more ofthe stimulation channels 129 during a stimulation frame.

The channel selector stage 150 may include any combination of hardware,software, and/or firmware as best serves a particular application.Moreover, the manner in which the channel selector stage 150 selects theone or more analysis stimulation channels 124 may vary as best serves aparticular application. For example, the channel selector stage 150 mayselect one or more of the analysis channels 124 that have the highestenergy levels as detected by the energy detection stages 126.Alternatively, the channel selector stage 150 may use a psychophysicalmodel, such as one utilized in MP3 audio compression, to select the mostrelevant analysis channels 124. In some examples, the channel selectorstage 150 sets the energy level of the unselected analysis channels 124to zero.

The number of analysis channels 124 selected by the channel selectorstage 150 may vary as best serves the particular stimulation strategybeing used. For example, in some stimulation strategies, the channelselector stage 150 is configured to select approximately one-half of theanalysis channels 124 for presentation to the patient. However, theratio of selected to unselected analysis channels 124 may be any numberas best serves the particular stimulation strategy being used. Moreover,the number of selected analysis channels 124 may vary from onestimulation frame to another.

Once one or more of the analysis channels 124 are selected by thechannel selector stage 150, the signals within each of the analysischannels 124 are input into a synthesizer stage 151. The synthesizerstage 151 is configured to combine the selected analysis channels 124that correspond to each stimulation channel 129 so that the informationcontained within the selected analysis channels 124 may be mapped tocorresponding stimulation channels 129. The selected analysis channels124 may be combined using any method as best serves a particularapplication. For example, the synthesizer stage 151 may be configured tosum the energy levels within each group of selected analysis channels124 that corresponds to a particular stimulation channel 129. Forexample, if two selected analysis channels 124 correspond to aparticular stimulation channel 129, the synthesizer stage 151 may beconfigured to sum the energy levels of the two selected analysischannels 124.

Once the selected analysis channels 124 corresponding to eachstimulation channel 129 are synthesized, the synthesized analysischannels 124 may be mapped to corresponding stimulation channels 129.

An exemplary stimulation strategy wherein the number of analysischannels is greater than the number of stimulation channels will now bedescribed in connection with FIG. 6. In particular, FIG. 6 is agraphical illustration of a process of selecting, synthesizing, andmapping a number of analysis channels 124 to corresponding stimulationchannels 129.

The first or left-most column of blocks shown in FIG. 6 represents anumber of analysis channels 124. Each block within the first columnrepresents a particular analysis channel 124. As shown in FIG. 6, anumber of the analysis channels 124 are represented with a hatch patternto indicate that they contain a particular energy level. It will berecognized that the energy level may be different for each of theanalysis channels 124.

In addition, a number of the analysis channels 124 within the firstcolumn may not have any energy level associated therewith. Such analysischannels 124 are represented by blocks not having the hatch pattern. Forexample, FIG. 6 shows three analysis channels 124 in the first columnthat do not have any energy level associated therewith.

As described previously in connection with FIG. 5, a channel selectorstage 150 may be configured to select one or more of the analysischannels 124 shown in the first column for presentation to a patient. Inother words, information contained within the one or more analysischannels 124 that are selected by the channel selection stage 150 isused to define stimulation current that is applied to the patient viaone or more of the stimulation channels 129 during a stimulation frame.

Hence, the second or middle column of blocks shown in FIG. 6 shows whichof the analysis channels 124 have been selected by the channel selectionstage 150. The selected analysis channels 124 are represented by blockswith hatch patterns within the second column. For example, as shown inFIG. 6, nine out of twenty analysis channels 124 have been selected bythe channel selection stage 150. It will be recognized that any numberof analysis channels 124 may be selected for presentation to a patient.

The manner in which the channel selector stage 150 selects the one ormore analysis stimulation channels 124 may vary as best serves aparticular application. For example, the channel selector stage 150 mayselect one or more of the analysis channels 124 that have the highestenergy levels.

In some examples, the energy levels of the unselected analysis channels124 are set to zero. In this manner, the unselected analysis channels124 may be included within the synthesis process. In other words, theunselected analysis channels 124 may be included within an averagingalgorithm used in the synthesis process. Alternatively, the unselectedanalysis channels 124 may be ignored during the synthesis process.

Once one or more of the analysis channels 124 have been selected forpresentation to a patient, the selected analysis channels 124 may besynthesized and mapped to corresponding stimulation channels 129. Thethird or right-most column of blocks shown in FIG. 6 represents a numberof stimulation channels 129. As shown in FIG. 6, each stimulationchannel 129 corresponds to a number of analysis channels 124. Forexample, each stimulation channel 129 shown in FIG. 6 corresponds tofour analysis channels 124, as indicated by the horizontal dashed lines.It will be recognized that each stimulation channel 129 may correspondto any number of analysis channels 124 as best serves a particularapplication. Moreover, it will be recognized that a particularstimulation channel 129 may correspond to a different number of analysischannels 124 than another stimulation channel 129. For example, a firststimulation channel may correspond to four analysis channels 124 and asecond stimulation channel may correspond to one analysis channel 124.However, it will be assumed that each stimulation channel 129corresponds to four analysis channels 124 in the examples given hereinfor illustrative purposes.

The selected analysis channels 124 may be synthesized using any suitablemethod as best serves a particular application. In some examples, theenergy levels within each group of selected analysis channels 124 thatcorresponds to a particular stimulation channel 129 are summed and/oraveraged. For example, if analysis channels labeled 124-1 through 124-4correspond to the stimulation channel labeled 129-1, synthesis may beperformed by summing the energy levels of the selected analysis channels124-1 and 124-4.

In some examples, as previously mentioned, the energy levels of theunselected analysis channels 124-2 and 124-3 may be set to zero. In thismanner, the synthesizer stage 151 may also include the unselectedanalysis channels (e.g., 124-2 and 124-3 in the summing function.

In some examples, none of the analysis channels 124 corresponding to aparticular stimulation channel 129 are selected for presentation to apatient. For example, none of the analysis channels 124 corresponding tothe stimulation channel labeled 129-2 shown in FIG. 6 have been selectedfor presentation to a patient. In some examples, the time framededicated to the stimulation channel 129-2 may be used to presentinformation for the next stimulation channel 129 that contains relevantenergy (e.g., the stimulation channel labeled 129-3. By so doing, thenet stimulation rate may be increased, which may be beneficial for somepatients.

Once the selected analysis channels 124 corresponding to eachstimulation channel 129 are synthesized, the synthesized analysischannels 124 may be mapped to corresponding stimulation channels 129. Bydividing the audio signal into more analysis channels 124 than there arestimulation channels 129, the likelihood that relevant informationwithin the audio signal will be included within the information that isselected for presentation to the patient increases. To illustrate, theaudio signal 140 of FIG. 4 is shown again in FIG. 7. However, as shownin FIG. 7, the audio signal 140 is divided into 32 analysis channelsinstead of into 8 analysis channels as shown in FIG. 4.

Because the audio signal 140 is divided into 32 analysis channels, eachanalysis channel shown in FIG. 7 is more narrow in bandwidth than eachanalysis channel shown in FIG. 4. Hence, a stimulation strategy thatselects the highest average energy-containing channels shown in FIG. 7for presentation to a patient will select channel 6, which contains thenarrow peak 141.

FIG. 8 is a flow chart illustrating an exemplary method of presenting anaudio signal to a patient with a cochlear implant system. The stepsshown in FIG. 8 are merely exemplary and may be omitted, added to,reordered, and/or modified.

In step 180, an audio signal is divided into a plurality of analysischannels 124. In some examples, as described previously, a number ofband-pass filters may be used to divide the audio signal into theanalysis channels 124. The total number of analysis channels 124 isgreater than the total number of stimulation channels 129 that arecoupled to or a part of the ICS 107.

In step 181, the energy level of the audio signal within each analysischannel 124 is detected. One or more energy detection stages 126 may beconfigured to detect the energy levels within each of the analysischannels 124. In some examples, the energy detection stages 126 areconfigured to calculate an average energy level within each analysischannel 124.

In some alternative examples, a masking function may be applied to theaudio signal prior to step 181. The masking function may be configuredto filter the audio signal and remove portions thereof that are notaudible to normal listeners. A variety of techniques may be used toperform the masking function as may serve a particular application.

Once the energy level of the audio signal within each analysis channel124 is detected, one or more of the analysis channels 124 may then beselected for presentation to the patient, as shown in step 182. Theparticular method used to select the analysis channels 124 may vary asbest serves a particular application. For example, one or more of theanalysis channels 124 having the highest average energy levels may beselected for presentation to the patient.

The selected analysis channels 124 may then be synthesized, as shown instep 183. In some examples, a synthesizer stage 151 is configured tosynthesize the selected analysis channels 124 by summing the detectedenergy levels within each group of selected analysis channels 124 thatcorresponds to each stimulation channel 129.

In step 184, the synthesized analysis channels are mapped to one or morestimulation channels 129. Stimulation current representative of theaudio signal may then be applied via one or more of the stimulationchannels 129 to one or more stimulation sites within the cochlea of thepatient.

The preceding description has been presented only to illustrate anddescribe embodiments of the invention. It is not intended to beexhaustive or to limit the invention to any precise form disclosed. Manymodifications and variations are possible in light of the aboveteachings.

1. A signal processing unit comprising: a plurality of filtersconfigured to divide an audio signal into a plurality of analysischannels; one or more detection stages configured to detect an energylevel within each of said analysis channels; a selection stageconfigured to select one or more of said analysis channels forpresentation to a patient; a synthesizer stage configured to synthesizesaid selected analysis channels; and a mapping stage configured to mapsaid selected analysis channels to a number of stimulation channelswithin an implantable cochlear stimulator; wherein a total number ofsaid analysis channels is greater than a total number of saidstimulation channels.
 2. The signal processing unit of claim 1, whereininformation within each of said synthesized analysis channels definesone or more stimulation current pulses delivered to a cochlea of patientvia said one or more stimulation channels during a stimulation frame. 3.The signal processing unit of claim 1, wherein each of said stimulationchannels corresponds to a group of one or more of said analysischannels.
 4. The signal processing unit of claim 3, wherein saidsynthesizer stage is further configured to synthesize said selectedanalysis channels by summing said energy levels of each of said selectedanalysis channels within each of said groups of said analysis channels.5. The signal processing unit of claim 1, wherein said plurality of saidanalysis channels comprises one or more analysis channels that are notselected for presentation to said patient, wherein said energy levels ofsaid selected analysis channels are greater than said energy levels ofsaid unselected analysis channels.
 6. A signal processing unitcomprising: one or more detection stages configured to detect an energylevel within each of a plurality of analysis channels corresponding to asingle stimulation channel; a selection stage configured to select asubset of the analysis channels for presentation to a patient based onthe detected energy levels; a synthesizer stage configured to synthesizethe selected subset of analysis channels; and a mapping stage configuredto map the synthesized subset of analysis channels to the singlestimulation channel.
 7. The signal processing unit of claim 6, whereinthe signal processing unit is configured to direct an implantablecochlear stimulator to apply a stimulation current to the patient viathe single stimulation channel in accordance with information containedwithin the synthesized subset of analysis channels.
 8. The signalprocessing unit of claim 6, wherein the synthesizer stage is configuredto synthesize the selected subset of analysis channels by summing thedetected energy levels of each of the analysis channels included in theselected subset of analysis channels.
 9. The signal processing unit ofclaim 6, wherein the synthesizer stage is configured to synthesize theselected subset of analysis channels by averaging the detected energylevels of each of the analysis channels included in the selected subsetof analysis channels.
 10. The signal processing unit of claim 6,wherein: the one or more detection stages are further configured todetect an energy level within each of an additional plurality ofanalysis channels corresponding to an additional single stimulationchannel; the selection stage is further configured to select anadditional subset of the additional analysis channels for presentationto the patient based on the detected energy levels of the additionalanalysis channels; the synthesizer stage is further configured tosynthesize the selected additional subset of analysis channels; and themapping stage is further configured to map the synthesized additionalsubset of analysis channels to the additional single stimulationchannel.
 11. The signal processing unit of claim 10, wherein the signalprocessing unit is configured to direct an implantable cochlearstimulator to apply a stimulation current to the patient via theadditional single stimulation channel in accordance with informationcontained within the synthesized additional subset of analysis channels.